Redundant Header.GetIndex() method

[AliceInHunterland]

Is your feature request related to a problem? Please describe.

It is preferable to avoid that, but generics in Go don't support structural types for now, ref. golang/go#51259.

// GetIndex returns the index of the block.
func (b *Header) GetIndex() uint32 {
	return b.Index
}

Describe the solution you'd like

So one day redundant code should be removed.

Describe alternatives you've considered

Additional context

#3789 (comment)

[AnnaShaleva]

Attach the link to the original conversation.